diff --git a/lib/mrkt/concerns/crud_leads.rb b/lib/mrkt/concerns/crud_leads.rb
index 529f6d0..054c250 100644
--- a/lib/mrkt/concerns/crud_leads.rb
+++ b/lib/mrkt/concerns/crud_leads.rb
@@ -1,5 +1,7 @@
 module Mrkt
   module CrudLeads
+    MAX_LEADS_SIZE = 300
+
     def get_leads(filter_type, filter_values, fields: nil, batch_size: nil, next_page_token: nil)
       params = {
         filterType: filter_type,
@@ -13,22 +15,30 @@ def get_leads(filter_type, filter_values, fields: nil, batch_size: nil, next_pag
     end
 
     def createupdate_leads(leads, action: 'createOrUpdate', lookup_field: nil, partition_name: nil, async_processing: nil)
-      post('/rest/v1/leads.json') do |req|
-        params = {
-          action: action,
-          input: leads
-        }
-        params[:lookupField] = lookup_field if lookup_field
-        params[:partitionName] = partition_name if partition_name
-        params[:asyncProcessing] = async_processing if async_processing
+      # see also: http://developers.marketo.com/documentation/rest/createupdate-leads/
+      # > You can update a maximum of 300 leads with a single API call.
+      leads.each_slice(MAX_LEADS_SIZE).map do |_leads|
+        post('/rest/v1/leads.json') do |req|
+          params = {
+            action: action,
+            input: _leads
+          }
+          params[:lookupField] = lookup_field if lookup_field
+          params[:partitionName] = partition_name if partition_name
+          params[:asyncProcessing] = async_processing if async_processing
 
-        json_payload(req, params)
+          json_payload(req, params)
+        end
       end
     end
 
     def delete_leads(leads)
-      delete('/rest/v1/leads.json') do |req|
-        json_payload(req, input: map_lead_ids(leads))
+      # see also: http://developers.marketo.com/documentation/rest/delete-lead/
+      # > The max batch size for this endpoint is 300 leads.
+      leads.each_slice(MAX_LEADS_SIZE).map do |_leads|
+        delete('/rest/v1/leads.json') do |req|
+          json_payload(req, input: map_lead_ids(_leads))
+        end
       end
     end
 
diff --git a/spec/concerns/crud_leads_spec.rb b/spec/concerns/crud_leads_spec.rb
index d446831..f41b925 100644
--- a/spec/concerns/crud_leads_spec.rb
+++ b/spec/concerns/crud_leads_spec.rb
@@ -72,7 +72,7 @@
         .to_return(json_stub(response_stub))
     end
 
-    it { is_expected.to eq(response_stub) }
+    it { is_expected.to eq([response_stub]) }
   end
 
   describe '#delete_leads' do
@@ -101,7 +101,7 @@
         .to_return(json_stub(response_stub))
     end
 
-    it { is_expected.to eq(response_stub) }
+    it { is_expected.to eq([response_stub]) }
   end
 
   describe '#associate_lead' do